Diffuse thyroid lesions are mainly inflammatory diseases of the thyroid gland, commonly known as subacute thyroiditis, Hashimoto’s thyroiditis, and acute thyroiditis. The main causes of diffuse thyroid lesions are as follows: 1. Subacute thyroiditis: usually caused by viral infection, the body will have fever and other symptoms of viral infection, and the thyroid gland will also appear painful nodules, the incidence of this disease is significantly more women than men, mostly in their 30s. 2. Hashimoto’s thyroiditis: also known as chronic lymphocytic thyroiditis, is an autoimmune disease of the body in which the patient develops an enlarged thyroid gland and hypothyroidism. It is usually an autoimmune reaction caused by a decrease in antigen-specific T-suppressor cells in the body, resulting in cytotoxic T cells that attack and destroy follicular cells. 3. Acute thyroiditis: Usually acute interstitial and septic inflammation caused by bacterial infection, but this disease is rare because the thyroid gland is more resistant to bacterial infection. Usually, diffuse thyroid disease is caused by several reasons such as the above, and patients need to pay attention to take active treatment in a timely manner.